Colouring matters of the Aphididae. Part XXXIV. Rhodo- and xantho-dactynaphins

Abstract

Rhodo- and xantho-dactynaphins undergo fission to form naphthaquinone derivatives related to the aphin pigments. Two different modes of fission occur, one under reductive conditions, the other on treatment with base. Structures are proposed for xantho- and rhodo-dactynaphins-jc-1. They resemble those of the aphins in consisting of two naphthalenic units coupled together but differ from them in that coupling is effected through carbon-oxygen rather than carbon–carbon bonds. The smooth rhodo ⇌ xantho interconversion is explained in terms of the reactivity towards nucleophiles of the 8-position in derivatives of 5,7-dihydroxy-1,4-naphthaquinone. Dactynaphins-jc-2 differ from the -jc-1 isomers in lacking a benzylic hydroxyl group. They contain the same nonaromatic side chain as the plant pigment, isoeleutherin.